5-heterocyclic-2,4-dialkyl-3H-1,2,4-triazole-3-thiones and their use as antidepressants

2,4-Dimethylthiosemicarbazide

To a stirred solution of methyl hydrazine (16.0 ml, 3.00×10 -1 mole) and sieve dry ethanol (50 ml) was added dropwise a solution of methyl isothiocyanate (22.0 g, 3.00×10 -1 mole) and sieve dry ethanol (30 ml). The reaction was exothermic and gently refluxed as the isothiocyanate was added. A precipitate soon formed. After stirring overnight, the reaction was cooled in an ice bath. The precipitate was then collected by filtration, washed with a little cold isopropanol, and dried by suction, affording a colorless solid: 26.7 g (75%). This material was crystallized two times from water and two times from isopropanol, affording small colorless needles: 14.7 g (41%), mp 135°-137° C.

Preparation of 1-(R n -Heterocyclyloyl)-R 2 , R 4 , -Substituted Thiosemicarbazides

1-(4-Pyridoyl)-2,4-dimethylthiosemicarbazide

To a stirred solution of 2,4-dimethylthiosemicarbazide (6.7 g, 5.6×10 -2 mole) and pyridine (150 ml) was added dropwise 4-pyridoyl chloride HCl (10.0 g, 5.62×10 -2 mole). After stirring for 17 hours the solvent was evaporated to dryness, affording a mixture of the desired 1-(4-pyridoyl)-2,4-dimethylthiosemicarbazide and pyridine hydrochloride. In general, this mixture was used without further purification in the subsequent cyclization step. If pure 1-(4-pyridoyl)-2,4-dimethylthiosemicarbazide is desired, the above mixture is treated with water and that which does not dissolve is collected by filtration. After drying by suction this material is crystallized.

2,4-Dimethyl-1-(2-thienoyl)thiosemicarbazide

To a stirred, room temperature, solution of 2,4-dimethylthiosemicarbazide (3.75 g, 3.15×10 -2 mole) and pyridine (30 ml) was added dropwise 2-thiophenecarbonyl chloride (3.20 ml, 2.99×10 -2 mole). After stirring overnight the pyridine was evaporated at reduced pressure and the concentrate was treated with H 2 O. The resulting semi-solid was extracted into ethyl acetate. The ethyl acetate extract was washed with saturated NaCl and subsequently dried over anhydrous Na 2 SO 4 . The drying agent was removed by filtration and the filtrate was evaporated at reduced pressure, leaving a slightly yellowish solid. This was treated with Et 2 O and the solid was collected by filtration affording a colorless powder: 4.7 g (68%), mp 176°-178° C.

Preparation of Final Products

5-(4-Pyridyl)-2,4-dimethyl-3H-1,2,4-triazole-3-thione

The 1:1 mixture from Example 2 and 1 molar aqueous NaHCO 3 (100 ml, 1.00×10 -1 mole) were stirred and warmed to reflux. After refluxing for 15 hours the reaction was allowed to cool in an ice bath. The resulting precipitate was collected by filtration and was dried by suction. The desired product was crystallized from ethyl acetate/hexane to yield large colorless plates: 4.1 g (35%), mp 150°-152° C.

2,4-Dimethyl-5-(2-thienyl)-3H-1,2,4-triazole-3-thione

A stirred mixture of 2,4-dimethyl-1-(2-thienoyl)thiosemicarbazide (4.7g, 2.0×10 -2 mole) and 1 molar aqueous NaHCO 3 (200 ml, 2.00×10 -2 mole) was heated to reflux for 6 hours. The reaction mixture was then placed in the refrigerator for several hours before the precipitate was collected by filtration. Crystallization from isopropanol afforded long colorless needles: 3.6 g (83%), mp 128°-129° C.

Other compounds embraced within formula I may similarly be prepared by using the procedures of Example 1-3 and substituting the appropriate Rn-heterocycloyl- and R 2 , R 4 -substituted reactants.

Using standard laboratory methodology, the pharmacological properties of the compounds, and their relative potencies, may readily be determined. When compared with other agents clinically known to be useful as antidepressants, the dosage regimen may readily be ascertained by those of ordinary skill in the art on the basis of the test results.

For example, the assay testing for prevention of reserpine-induced ptosis in mice and in rats is a standard assay. In those test groups, weighed mice or rats are housed individually in wire mesh stick cages and administered test compound or vehicle. At a selected time thereafter, reserpine, prepared as a 4 mg/ml solution in dilute acetic acid, is given to rats at a dose of 4 mg/kg subcutaneously, and to mice as a 0.2 mg/ml solution in dilute acetic acid at a dose of 2 mg/kg intravenously into a tail vein. In each assay the animals are examined individually in a plexiglass cylinder 90 minutes later in the rat assay or 60 minutes after administration of reserpine to mice. Prevention or delay of ptosis is considered significant if the average closure of both eyes is less than 50% after observing for 30 seconds. The ED 50 for prevention of ptosis is defined as the dose of test compound that significantly prevents ptosis in 50% of the test animals.

Another assay utilized to evaluate antidepressant activity is testing for the antagonism of RO-4-1284* -induced hypothermia. (*Niemegeers, Carlos, J. E. "Antagonism of Reserpine--Like Activity", edited by S. Fielding and H. Lal, published by Futura, pg. 73-98.) In this test, groups of male mice are weighed and housed individually in wire mesh stick cages. The rectal temperature of each mouse is recorded and the test compound or vehicle is then administered. At a selected time thereafter, RO-4-1284, prepared as a 2 mg/kg solution in distilled water, is administered at a dose of 20 mg/kg i.p. Mice are then placed in a cold room (36° F.) for 30 minutes, and then returned to room temperature for 30 minutes. At this time (60 minutes after RO-4-1284 administration) the rectal temperature of each mouse is again recorded. Under these conditions, RO-4-1284 causes a fall in rectal temperature of more than 6° C. The final temperatures of control groups of ten RO-4-1284-treated mice from a number of experiments are combined to form an "historic control" of 100 mice. This control is updated periodically by replacement of the oldest data. Any drugtreated animal which has final temperature (after RO-4-1284) which is greater than the mean +2 S.D. of the RO-4-1284 historic control is considered to exhibit significant antagonism to the hypothermic effect of RO-4-1284. The ED 50 for antagonism is defined as that dose of test compound which significantly antagonizes RO-4-1284 hypothermia in 50% of the test animals.

These standard laboratory tests demonstrate that the compounds of this invention have pharmacological effects generally attributed to anti-depressants and thus the compounds of this invention will elevate mood in patients suffering from depression and will have an end-use application in the treatment of patients suffering from endogenous depression, a term used interchangeably with psychotic or involutional depression. In this use, the compound (I) will exert a relatively quick onset of action and have a prolonged duration of activity. In general, the compounds may be expected to exert their antidepressant effects at dose levels of about 0.25-25 mg/kg of body weight per day although, of course, the degree of severity of the disease state, age of the patient and other factors determined by the attending diagnostician will influence the exact course and dosage regimen suitable for each patient. In general the parenterally administered doses are about 1/4 to 1/2 that of the orally administered dose.

For oral administration, the compounds can be formulated into solid or liquid preparations such as capsules, pills, tablets, troches, powders, solutions, suspensions or emulsions. The solid unit dosage forms can be a capsule which can be of the ordinary gelatin type containing, for example, lubricants and inert filler, such as lactose, sucrose or cornstarch. In another embodiment, the compounds of general formula I can be tableted with conventional tablet bases such as lactose, sucrose and cornstarch, in combination with binders, such as acacia, cornstarch or gelatin, disintegrating agents such as potato starch or alginic acid, and a lubricant such as stearic acid or magnesium stearate.

For parenteral administration, the compounds maybe administered as injectable dosages of a solution or suspension of the compound in a physiologically acceptable diluent with a pharmaceutical carrier which can be a sterile liquid such as water, alcohols, oils and other acceptable organic solvents, with or without the addition of a surfactant and other pharmaceutically acceptable adjuvants. Illustrative of oils which can be employed in these preparations are those of petroleum, animal, vegetable, or synthesic origin, for example, peanut oil, soybean oil and mineral oil. In general, water, saline, aqueous dextrose and related sugar solutions, ethanol, and glycols such as propylene glycol or polyethylene glycol or 2-pyrrolidone are preferred liquid carriers, particularly for injectable solutions.

The compounds can be administered in the form of a depot injection or implant preparation which may be formulated in such a manner as to permit a sustained release of the active ingredient. The active ingredient can be compressed into pellets or small cylinders and implanted subcutaneously or intramuscularly as depot injections or implants. Implants may employ inert material such as biodegradable polymers or synthetic silicones, for example Silastic®, a silicone rubber manufactured by the Dow-Corning Corporation.

As is true in many classes of compounds with a pharmacological activity having a therapeutic end-use application, certain subgeneric groups and certain specific members of the class, because of their overall therapeutic index and their biochemical and pharmacological profile, are preferred. In this instance the preferred compounds are those wherein both R 2 and R 4 groups are methyl or ethyl, those wherein the Rn heterocyclic group is 4-, 3- or 2-pyridyl, or 2- or 3-thienyl.